This invention relates to particle counting apparatus and more particularly to apparatus and a method for counting particles such as blood cells suspended in a liquid medium.
In the medical field, particle counters are used, for example, to count white blood cells in a sample of a patient's blood with the resultant count value used in making a diagnosis. Many techniques have been employed in particle counting, among these being colorimetry, microscope counting using a chamber, light scattering from particles in non-coaxial or coaxial (sheath) flow and aperture conductivity counting. Representative patents in which this latter technique is disclosed are U.S. Pat. Nos. 2,656,508 and 2,869,078. In addition, some particle counters using aperture conductivity counting also introduce air bubbles into the flow stream of a sample to separate the sample into two or more portions and the volume of these portions, for which a particle count is made, is metered by use of electro-optical gating circuits. A representative patent in which this technique is disclosed is U.S. Pat. No. 3,657,725.
These previously developed counters all require pumps, solenoids or motors and are quite costly, bulky in size and must be supplied with power from typical utility sources. Additionally, the test procedures which must be followed in using one of these counters to obtain accurate results are typically involved and complex. Thus, such counters are usually found only in a hospital or a laboratory. This complicates and unduly lengthens a physician's task of diagnosing a patient's illness when he thinks a cell count should be made for a sample of the patient's blood because he must take a blood sample from the patient, tag it, send it to a laboratory for testing and then await the test results before prescribing a course of treatment for the patient.